PHOENIX — As a general rule, Senator John McCain does not alert the news media when he eats breakfast in Arizona.

But on a Monday morning this month, Mr. McCain campaigned in a local diner, after a Sunday stop at his campaign office here, where he urged volunteers to “make sure we get our voters registered, to make sure we are organized.”

In the sea of uncertainty that defines American politics, presidential candidates have generally been able to count on the residents of their home state, Al Gore’s loss of Tennessee in 2000 being a notable exception.

But a variety of factors have made Mr. McCain’s chances in Arizona less assured than they ordinarily would seem, which his campaign has acknowledged.

The number of independent voters in Arizona has risen 12 percent since 2004, and those voters have helped send a Democrat to the governor’s mansion and given the party four of the state’s eight Congressional seats — including two in 2006, one in a historically Republican district.

At the same time, Arizona Democrats, like many of their counterparts around the country, have outpaced Republicans in voter registration, adding almost 20,000 voters to the rolls since March, compared with the Republican majority’s 8,600 new voters. The second-term Democratic governor, Janet Napolitano, remains wildly popular.

Added to list of 'battleground states'Last month, the McCain campaign startlingly added Arizona to its list of 24 “battleground states,” a fact that state Democrats have clung to like sprinkles on a soft-serve ice cream cone.

“John McCain has striking vulnerabilities here,” said Emily DeRose, spokeswoman for the Arizona Democratic Party. “We are going to take him to the mat. We are not giving him a pass in Arizona.”

What is more, the state’s Republican Partyis more or less in disarray, split between its moderate and staunchly conservative factions. Its chairman, who cheerfully attended a Ron Paulcampaign event here just two months ago, has been a thorn in Mr. McCain’s political side for years. On Super Tuesday, Mr. McCain captured 47 percent of his party’s voters, hardly the resounding victory that a candidate who has represented his state for over 25 years might expect.

The Democratic ambitions may be largely bluster. Neither Mr. McCain nor Senator Barack Obama, his presumed rival this fall, appears to be spending money in the state. There are no advertisements, and the Obama campaign has no paid staff here.

Mr. McCain’s political director, Sarah Simmons, said the campaign’s designation of Arizona as a battleground state was simply a recognition that voters there do not always vote for Republicans for president.

“Obviously, any state that has swung before, we pay attention to,” Ms. Simmons said. (Arizona has gone to the Democratic presidential candidate twice since 1948 — Harry S. Trumanwon it that year, and Bill Clintonin 1996.)

'Disenfranchised' RepublicansMr. McCain’s recent visit to his southwest regional campaign headquarters here to cheer on volunteers and his breakfast photo op were unusual for an election with so many states in play.

Mr. McCain may be trying to appeal to people like Steven Townsend, a software executive from the upscale Paradise Valley neighborhood of Phoenix, who said he had voted for Mr. McCain several times.

“I represent a large group of Republicans in this state who feel disenfranchised,” Mr. Townsend said, citing the war, the economy and Mr. McCain’s occasional forays into socially conservative territory as reasons for his disenchantment.

“You’ve got such a large percentage of the population that is here now that doesn’t care about the popular history that many here have about him,” he said. “I believe he is susceptible here. It is not as clear-cut as some people may believe.”

Latinos and young votersIndeed, demographic trends may not favor Mr. McCain. Roughly 20 percent of the state’s voters are Latino, a group that tends to support Democrats in this state. Many Republicans in Arizona, including the sheriff of the most populous county, have taken an extremely hard line on illegal immigrants.

Further, there has been a large influx of younger voters, who tend to favor Democrats over Republicans by about two to one, said Bruce D. Merrill, a state polling expert. Many of these people are registering for the first time.

“I’ve never voted, and I never cared to vote,” said Sandy Simmons, 28. “But this is such an exciting time in our history.” She said she planned to vote for Mr. Obama.

Also, Mr. McCain’s state party has not been his staunchest supporter. It recently came under the control of its most conservative, activist branch, which was infuriated last year by Mr. McCain’s support of a Senate bill that would have offered a pathway to citizenship for illegal immigrants. The state Republican chairman, Randy Pullen, has often shown support for other candidates, and he attended a rally for Mr. Paul in late May.

“He is the best pick almost by luck of the draw,” Mr. Pullen said of Mr. McCain in an interview at the party’s headquarters here.

Mr. Pullen shrugged off the many disparaging remarks he had made about Mr. McCain in the past, most revolving around what he saw as the senator’s lack of conservative credentials. “That was then, this is now,” he said. “At this point, I very much support John McCain.”

Crossover votesMr. McCain’s more relevant concern in this state may be the independents, who have been registering at a breakneck speed since the last presidential election and who, along with crossover Republicans, clearly helped elect Democrats in 2006.

For example, while registered Democrats accounted for only 33 percent of voters in 2006, Ms. Napolitano won re-election with 63 percent of the vote. In the state’s Fifth Congressional District — which Republicans had controlled since 1985 — a Democrat, Harry Mitchell, unseated the Republican incumbent, J. D. Hayworth, even though only 27 percent of voters were registered Democrats then, the same percentage as Republican voters. A similar dynamic drove the race in the Eighth Congressional District, where a Democrat prevailed in a race for an open seat.

“My research shows that in Arizona, the new independent is a different type of person from seven years ago,” said Mr. Merrill, the polling expert. “That voter was more libertarian, more get-government-out-of-my-life. The new independents, which went heavily Democratic in the last election, are much younger, better educated and overwhelmingly antiwar.”

While Democrats welcomed the McCain campaign’s description of Arizona as a battleground state, the pronouncement could also have been a strategic move, done to raise money or motivate volunteers at home, or to mess with the minds of the opposition.

“I didn’t take that too seriously,” said Mr. Pullen, the Republican chairman. “I probably should have called them to ask why. It could have been a trap for Obama.”

Ms. Simmons, the McCain staff member, said the lack of resources being shown by both campaigns was an indicator that there was no real race in Arizona.

“I think it would be a real stretch to say Arizona is a battleground state for us,” she said, “just as it would be a stretch to say Illinois is a battleground state for Obama.”